Stubbing returns null with named argument mixed ordering

[Th4n]

I'm not sure whether it's mockito-kotlin as it seems that something is wrong on boundary of kotlin/mockito, however it might be a thing that mockito-kotlin can solve somehow.

It seems like that using named arguments that are ordered in a different way compared to method signature breaks stubs so they return nulls only. Once I managed to get a class cast exception as Mockito was trying to cast my Arg2 into Arg underneath, however now I'm not able to reproduce it.

Here are couple of tests showing this behaviour

    @Test // failing
    fun `reverse order stub`() {
        val arg = Arg()
        val arg2 = Arg2()

        val pointFactory: PointFactory = mock()
        whenever(pointFactory.newInstance(y = any(), x = any())).thenReturn(mock())

        val result = pointFactory.newInstance(arg, arg2)

        Truth.assertThat(result).isNotNull()
    }

    @Test // failing
    fun `reverse order stub, reverse invocation`() {
        val arg = Arg()
        val arg2 = Arg2()

        val pointFactory: PointFactory = mock()
        whenever(pointFactory.newInstance(y = any(), x = any())).thenReturn(mock())

        val result = pointFactory.newInstance(y = arg2, x = arg)

        Truth.assertThat(result).isNotNull()
    }

    @Test
    fun `regular order stub, regular invocation`() {
        val arg = Arg()
        val arg2 = Arg2()

        val pointFactory: PointFactory = mock()
        whenever(pointFactory.newInstance(x = any(), y = any())).thenReturn(mock())

        val result = pointFactory.newInstance(arg, arg2)

        Truth.assertThat(result).isNotNull()
    }

    @Test
    fun `regular order stub, reverse invocation`() {
        val arg = Arg()
        val arg2 = Arg2()

        val pointFactory: PointFactory = mock()
        whenever(pointFactory.newInstance(x = any(), y = any())).thenReturn(mock())

        val result = pointFactory.newInstance(y = arg2, x = arg)

        Truth.assertThat(result).isNotNull()
    }

    class Arg
    class Arg2

    class Point

    class PointFactory {

        fun newInstance(x: Arg, y: Arg2): Point {
            return Point()
        }
    }

Also on mockito issue tracker: https://github.com/mockito/mockito/issues/1413

[StormeHawke]

I'm seeing the same issue

[linkrjr]

Same here. Any ideias?

[tim-phillips]

Just encountered this, very hard to debug.

[rasmusandersson5]

Yep, this was a nasty one... Makes refactoring quite cumbersome if you can't use named arguments...

[bohsen]

I don't think this has been mentioned, but this AFAIK is a java-kotlin interop issue. Kotlin named parameters is a pure Kotlin concept. It is not present in Java which means interoperability is not possible. Mockito-kotlin is still just a wrapper around Mockito(the java library).

Maybe someone with time on their hands should add a section on "Known limitations" to the readme and add this as a gotcha.

[StormeHawke]

You can't use named parameters on Java methods, only on kotlin. It should be possible to rearrange passed parameters the same way kotlin.lang does under the hood to support this

[bohsen]

@StormeHawke The problems lies in the stubbing. When you stub a function of a mock, the call can have an arbitrary number of parameters of various types. How would you go about rearranging them? Another issue could be detecting if you're using a matcher or not.

As an example look at how whenever is implemented:

/**
 * Enables stubbing methods. Use it when you want the mock to return particular value when particular method is called.
 *
 * Alias for [Mockito.when].
 */
@Suppress("NOTHING_TO_INLINE")
inline fun <T> whenever(methodCall: T): OngoingStubbing<T> {
    return Mockito.`when`(methodCall)!!
}

whenever delegates the call directly to Mockito.

[StormeHawke]

We're software engineers. If our job was easy anybody could do it 😉

[tianyanz]

Is there any plan to fix this?

[edwardmp]

Just spent 2 hours diagnosing why my mock kept returning null. I appreciate it might not be easy to solve but very cumbersome to stumble upon this.

[tomas0svk]

+1

[AlexRP239]

This is quite difficult to fix since mockito stores matchers in the stack as it defined in the when or verify block. And kotlin's variables by name just a syntactic sugar. So you need to always write all parameters (even with default values) in real order as it it in runtime or don't use argument matchers at all.